1. Field of the Invention
The present invention relates to a three-dimensional shape of a blade used in an axial-flow rotary fluid machine such as an axial-flow turbine and an axial-flow compressor, and particularly to a blade having an extremely small aspect ratio.
2. Description of the Related Art
An airfoil of a turbine blade of an axial-flow turbine described in Japanese Patent Application Laid-open No. 2002-138801 includes an inflection point between an upstream concave portion and a downstream convex portion in the rear of an 80% position on an intrados, so that a shock wave generated from the intrados of a trailing edge is dispersed into two components by the effect of the inflection point to weaken the respective shock wave components, thereby decreasing the energy loss generated due to the interference of these shock wave components with a boundary layer of an extrados of an adjacent turbine blade. In this blade airfoil, a camber line in the vicinity of the trailing edge is curved in an S-shape by the provision of the inflection point on the intrados in the vicinity of the trailing edge.
A turbine blade having a low aspect ratio has a significant tendency (a secondary flow) that the flow of a fluid along a blade surface is deflected from the side of a blade tip toward a blade root, resulting in a problem of an increased pressure loss in the blade. In the above-described conventional blade, however, a three-dimensional shape of the turbine blade, namely, a difference between the airfoil of the blade root and the airfoil of the blade tip is not taken into consideration, so that the pressure loss accompanying the secondary flow cannot be sufficiently decreased.